Tamil Nadu State is situated at the South-eastern extremity of the Indian Peninsula, bounded on the east by the Bay of Bengal, Western Ghats on its west, Indian Ocean on its south and Nellore and Chittoor districts of Andhra Pradesh and Kolar, Bangalore and Mysore districts of Karnataka State on the northwest. It has a coastal line of 922 km and land boundary of 1200 km. It lies between 8° 5΄ and 13° 35΄ N latitude and between 76° 15΄ and 80° 20΄ E longitude. The State can be divided into two natural divisions namely, the coastal plains and hilly western areas. The Palaghat gap of Kerala about 25 km in width in the great western mountain wall is the only marked break to Tamil Nadu. The slopes of the Western Ghats are covered with heavy ever green forests, that too presently being made grey rapidly with human intervention, thus making susceptible for animal and human conflict.
The trend of drainage is from west to east into the Bay of Bengal. The river Cauvery rises from the Brahmagiri hill in Coorg district of Karnataka and passes across eastwards across the peninsula into the Bay of Bengal. The Ponnaiyar River rises from Kolar district of Karnataka runs across the State and falls into the sea north of Cuddalore. The Vaigai river from Western Ghats and passes across the State and finally falls into the Bay of Bengal, 16km east of Ramanathapuram.
The Proximity of sea influences the climate of the eastern and southern parts of the state whereas hilly orography and inland locations play important roles in modifying the climate over rest of the State. The western portions of the State and the portions bordering with Kerala are fall under the climate type, Marine, mild winter, moist all seasons, warm summer and the remaining part of the State comes under the climate type: Tropical Savanna, Hot, seasonally dry (Aw). Out of 13 million hectares of geographical area, about 7 million hectares of land is under cultivation. The farming situation covers irrigated (55%) and rain fed / dry land (45%).Among all States of India, ground water has been harnessed fully in the State of Tamil Nadu.
Out of 15 agro-climatic zones of India as per Planning Commission of India, Tamil Nadu comes under two zones, namely Southern Plateau and Hills region (AC.10) and East Coast and Hills region (AC.11). Under National Agricultural Research Project of ICAR, with in the broad classification of Planning Commission’s 15 agro-climatic zones (AC10&11), Tamil Nadu has been divided in to seven agro climatic sub-zones and those are North western zone.
o North eastern zone,
o western zone,
o Cauvery Delta zone,
o Southern zone,
o High rainfall zone and
o High Altitude and o Hilly zone.
Against the agro-climatic zones concept, the National Bureau of Soil Survey and Land Use Planning, Nagpur has brought Tamil Nadu under three agro-ecological zones namely, Hot semi arid eco- region with red loamy soil (AER8), Hot sub humid to semi arid eco- region with coastal alluvium derived soils (AER18) and Hot humid-per humid eco-regions with red lateritic and alluvium derived soils (AER19). Further, within these three agro-eco regions, the National Bureau of Soil Survey and Land Use Planning, Nagpur again divided Tamil Nadu in to 16 agro-ecological sub zones. Hence planning should be made on these boundaries.
Rainfall Pattern
The State mainly receives its rainfall in three seasons, viz. South west Monsoon (SWM), North east Monsoon (NEM) and Pre monsoon season. The normal annual rainfall falling over the state is 958.4 mm is received at the State. About 48 per cent of the total annual average rainfall is received during NEM, while about 35 per cent is received during SWM and the balance in the other seasons. Tamil Nadu receives about 51 per cent of its annual rainfall during NEM season. The coastal districts receive about 65 – 75 per cent of annual rainfall and interior districts get about 40-50 per cent in this season. The percentage share of rainfall of different locations coastal/ inland / hilly stations for four seasons are given in the Table 4.1.From the table, it can be seen that the percentage share of rainfall during the NEM is higher in most parts of Tamil Nadu. The hilly regions in the west and hilly/ plain lands in north western half of the region only receive major share from SWM.
Temperature
In general the maximum temperature rarely exceeds 43° C and the minimum temperature rarely downs below 18° C. The mean annual temperature is 28.2°C in the plains and 15.2°C in the hills. The temperature is minimum in the month of December with 24.7°C and maximum in May with 37.3°C. Soil temperature data available for a few places indicate a range from 30.7°C to 32.3°C in the plains and around 14.4°C in the hills. On the basis of temperature the coastal plain (Aduthurai) is classified as hyper-thermic (very hot), northern part (Coimbatore) and southern part (Kovilpatty) are iso-hyperthermic (steadily very hot) and hill area (Uthagamandalam) is iso-mesic (steadily cold).
Monsoons Onset and Withdrawals
The normal onset of Southwest (SW) monsoon over Tamil Nadu is predicted to take place on 1st June with a standard deviation of 7.4 days (based on data of 1901-2011). During the last 31years (1981-2011) period, however, the normal date has advanced by a day with SD of 6 days. The earliest onset is 11th May and the late onset is 18th June. Based on the linear trend analysis, it was found that the onset is advanced by one day in every 20 years period (1901-2011). The Northeast monsoon (NE monsoon) sets in over Tamil Nadu on 20th October (based on 1901- 2000).
The earliest onset is 4th October and late onset is 11th November. In 75 per cent of years, the onset of NE monsoon took place between 13th October and 27th October. In 8 per cent of years the monsoon onset was found in November month. Northeast monsoon withdraws from Tamil Nadu on 30th December with SD of 14 days. IN 51 per cent of the years, the withdrawal is between 14th December and 4th January. IN 2 per cent of the years the withdrawal took place in November itself. IN 40 per cent of the years, the withdrawal occurred in January month.
- TNPSC Mains Tests and Notes Program
- TNPSC Prelims Exam 2020- Test Series and Notes Program
- TNPSC Prelims and Mains Tests Series and Notes Program
- TNPSC Detailed Complete Prelims Notes